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Old 01-16-2023, 10:18 AM   #1 (permalink)
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Air Ball in Pickup Bed and Bucket Headlight

Cd's post on another thread caused me to think
Let's do a different think...
The back of a pickup is a cavity; the bucket headlight is a cavity. The pickup's least resistance is with the tailgate up which allows the air to form a ball in the bed of the pickup, around which the air flows with least resistance.
The bucket headlight perhaps acts like the bed of the pickup, but on a smaller scale. A ball forms in the bucket and the air flows around the ball with least resistance.

Does this make sense to anyone else?

My best skills were used on the illustration...

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Old 01-16-2023, 11:39 AM   #2 (permalink)
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Works for me. Air is also compressible so could mold flow for most laminar
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Old 01-16-2023, 01:54 PM   #3 (permalink)
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anyone else

Quote:
Originally Posted by Joggernot View Post
Cd's post on another thread caused me to think
Let's do a different think...
The back of a pickup is a cavity; the bucket headlight is a cavity. The pickup's least resistance is with the tailgate up which allows the air to form a ball in the bed of the pickup, around which the air flows with least resistance.
The bucket headlight perhaps acts like the bed of the pickup, but on a smaller scale. A ball forms in the bucket and the air flows around the ball with least resistance.

Does this make sense to anyone else?

My best skills were used on the illustration...
They both create a 'phantom' effect, but I'd want to mention some qualifiers.
1) up front, all the air 'attacking' the forebody is within a 'favorable' pressure gradient. It's all flowing towards a region of lower pressure.With just a bare minimum of edge radii, the air will flow around the front as if perfectly streamlined.
2) in the aft-body of the pickup, there's an airtight rear-facing step which both triggers flow separation, and creates the iconic captured-vortex when the tailgate is closed.This vortex doesn't exist in the front, 'over' the headlight bucket. There's just dead air pooling ahead of the entire nose,creating the 'phantom' pointed nose, as illustrated in Lanchester's streamline body of revolution, 1907.
You can see it taking form ahead of Kamm's K-car of circa 1937
https://ecomodder.com/forum/member-a...-kamm-back.jpg
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Old 01-16-2023, 02:16 PM   #4 (permalink)
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Not to nit-pick your art, but....

Air being compressible fluid, the 'ball' of air will be a half-ball shape.

An interesting phenomenon is that big trucks on I-5 in the rain will have a cylindrical plume of water and air projecting outward from the front wheelwells well into the pressure gradient. The air is entrained by the rotating tire.
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Old 01-16-2023, 03:04 PM   #5 (permalink)
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'compressible'

I need to mention that, compressibility effects do not begin until around 250-mph. Until then, air is considered an incompressible fluid, the reason why aerodynamics is just a branch of fluid mechanics.
The 'ground' is the 'ocean floor' of the troposphere. Our cars are fully-submerged structures, completely surrounded by 'fluid.'
When we move, we 'displace' air, but we don't compress it.
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Old 01-16-2023, 03:15 PM   #6 (permalink)
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T'would be a good test case for tuft testing. Do tufts at the leading edge of the bucket stand up in the air?

What happens when two incompressable flows intersect?
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Old 01-16-2023, 04:37 PM   #7 (permalink)
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tufts / intersect

Quote:
Originally Posted by freebeard View Post
T'would be a good test case for tuft testing. Do tufts at the leading edge of the bucket stand up in the air?

What happens when two incompressable flows intersect?
* If there is the minimum required radius surrounding the bucket ( top and side ), the air (tuft ) will be slammed against the surface, and pinned there by the attacking flow.
* The outcome of intersecting flows depend completely on the topography of their adjacent surface, local velocity, density, pressure, direction; upstream, downstream, above, below, axially in the boundary layer, and beyond, into the nearest local streamline. It's extremely conditional.
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Old 01-16-2023, 05:47 PM   #8 (permalink)
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I can't really make out what is happening in the headlight area, but found these two really good tuft tests on a current generation Camaro on YouTube :
https://youtu.be/fzN5InPImT4


https://youtu.be/o2iCVef2VIw


I find the frame rate hilarious, since the wheels appear to be not even moving LOL.

Last edited by Cd; 01-16-2023 at 09:24 PM..
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Old 01-16-2023, 06:07 PM   #9 (permalink)
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At this permalink [#1152] aerostealth posted a video with a segment on how NACA ducts are suboptimal.

Disappionted to say the least, but the original design had fences and a rolled lip.
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Old 01-16-2023, 07:01 PM   #10 (permalink)
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Quote:
Originally Posted by freebeard View Post
At this permalink [#1152] aerostealth posted a video with a segment on how NACA ducts are suboptimal.

Disappionted to say the least, but the original design had fences and a rolled lip.
Viewing this on my Android phone.
Clicking the permalink takes me to a page, then immediately goes to some other thread.
In this case, it brought me to a post on YouTube creator 'SuperfastMatt' 's video on backwards aerodynamics.

So a little glitch there.

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